1. Field of the Invention
The present invention relates to assembling electrochemical cell components. More particularly, the invention relates to using a bonding agent such as cements, glues, solders, adhesives and the like to bond components or subassemblies of an electrochemical cell or stack.
2. Description of the Related Art
Conventional construction of fuel cell stacks, electrolyzer stacks, or gas (hydrogen or oxygen) concentrator stacks, especially proton exchange membranes (PEM) stacks, requires a large number of substantially flat or planar components or subassemblies (including bipolar plates, flowfields, membrane and electrode assemblies, and, optionally, cooling plates) to be assembled between a pair of heavy metal endplates. The entire assembly is normally placed in compression, much like a filter press, through the use of a series of long threaded metal rods (tie rods) extending from one endplate of the assembly to the other endplate, with nuts or other fasteners on either end. The compression forces exerted through the tie rods normally compress a gasket, o-ring or similar device that is inserted between the sealing surfaces, thereby sealing any gases or liquids inside the electrochemical cell stack.
Electrochemical stacks are beginning to include adhesives for bonding the electrochemical cell stack components together, without the need for heavy endplates, tie bars, gaskets or o-rings. The adhesive bonds the components together and seals the gases and/or liquids inside the electrochemical cell stack. The resulting electrochemical cell stack is much lighter and smaller than a traditional stack. While each o-ring and gasket is not heavy itself, these components nevertheless increase the size, weight and complexity of an electrochemical stack due to design constraints related to the use of seals such as o-rings and other elastomers.
Thermoplastic adhesives are often the preferred adhesives for bonding the parts of an electrochemical cell stack. These adhesives must be heated in an oven for curing after being applied to the components. Other adhesives that may be used include reactively cured adhesives and solvent loss adhesives. However, regardless of the type of bonding agent (adhesive, glue, cement, solder, or the like) used, the components must be held in place while the bonding agent dries or is cured. Many types of clamps and jigs are used to hold the components in place or alternatively, the weight of the components themselves may be sufficient to hold the components together while the adhesive cures. Often, the clamps are so large and bulky that the components cannot be placed in an oven for the adhesive to cure. Applying the adhesive quickly, while keeping the adhesive away from areas where the adhesive may clog or otherwise damage the components, is quite difficult. It is also a problem to keep the components properly compressed during storage of component assemblies before the components are heated in an oven for proper adhesive curing. Furthermore, it is a problem to keep the adhesive from running to undesirable areas while it is in the oven. The present invention provides a solution to these problems.
Therefore, there is a need for a method and apparatus for assembling electrochemical cell components and subassemblies that facilitates the use and application of a bonding agent between the components. It would be desirable if the method and apparatus were simple to perform and operate, yet made efficient use of equipment that is found in a common laboratory. It would also be desirable if the method enabled both the assembly of custom components and subassemblies and large-scale assembly-line production of electrochemical cell components into bonded unitary structures
The present invention provides a method of assembling electrochemical cell components, comprising aligning first and second electrochemical cell components; providing a bonding agent between the first and second electrochemical cell components; placing the aligned components into a container consisting essentially of a pliable bag; and drawing a vacuum within the pliable bag, wherein the pliable bag molds to a shape of the aligned components. The method may further comprise applying pressure to the outside of the vacuum bag, wherein the pressure is selected from hydrostatic pressure and pneumatic pressure, or placing the sealed vacuum bag containing the components into an oven. Optionally, the method may further comprisedistributing the bonding agent through one or more closed channels formed between the first and second electrochemical cell components. The optional step of distributing the bonding agent through one or more closed channels may further comprise adding the bonding agent into an upward-facing open channel in the bonding surface of the first component; creating the closed channel when the second component is aligned with the first component; and inverting the components, wherein the bonding agent flows against the second component by means selected from gravity, capillary action and combinations thereof. A plurality of supports may be disposed in the open channel or in the second component, wherein the method further comprises supporting a section of the second component that covers the open channel; supporting the open channel, wherein the first and second components do not deform from pressure exerted by the pliable bag.
The step of distributing the bonding agent through a channel further comprises adding a bonding agent into the closed channel though one or more fill ports, wherein the one or more fill ports are in fluid communication with the closed channel. The bonding agent source is a syringe, pump, or other delivery device having a conduit adapted to form a seal with each of the one or more fill ports, the method further comprising injecting a bonding agent into the closed channel from the delivery device. Optionally, an overfill reservoir is provided in fluid communication with the closed channel, the method further comprising capturing excess bonding agent flowing from the closed channel into the overfill reservoir.
The invention also provides a subassembly of electrochemical cell components, comprising a first component having a first bonding surface with one or more open channels, wherein the one or more open channels contain a bonding agent; and a second component having a second bonding surface aligned with the first bonding surface of the first component. Optionally, the subassembly may further comprise a plurality of supports disposed within the one or more open channels or extending from the second bonding surface, wherein the supports prevent the atmospheric or applied external pressure from deforming the first component or the second component along the one or more open channels. Preferably, the subassembly also includes a bonding agent delivery reservoir in fluid communication with the one or more channels, and a bonding agent disposed in the reservoir. Optionally, the bonding agent reservoir is adapted to expose the bonding agent to externally applied fluid pressure. An overflow reservoir may also be included in fluid communication with an opposing end of the one or more channels from the bonding agent reservoir. In one embodiment, the subassembly has opposing bonding surfaces on the first and second electrochemical cell components, wherein the bonding surfaces have been treated to enhance flow of the bonding agent; and opposing non-bonding surfaces on the first and second electrochemical cell components, wherein the non-bonding surfaces have been treated to inhibit flow of the bonding agent. Optionally, the bonding surfaces may be treated by a process selected from applying a wetting agent, polishing, etching and combinations thereof. Separately, the non-bonding surfaces may be treated by a process selected from roughening, chemically modifying, coating, and combinations thereof. The non-bonding surfaces may be coated with polytetrafluoroethylene (PTFE) or perfluoroalkoxy (PFA). Furthermore, the bonding surfaces may have a plurality of surface features, such as micro grooves. Preferably, the method includes maintaining alignment of the cell components by interlocking one or more feature between the first and second cell components, where an exemplary interlocking feature is a pin.
Finally, the invention provides a method of assembling electrochemical cell components, comprising aligning first and second electrochemical cell components; providing a bonding agent between the first and second electrochemical cell components; placing the aligned components into a pliable bag; placing the pliable bag within a vacuum chamber; and drawing a vacuum on the vacuum chamber. The method may further comprise sealing the bag to retain the vacuum within the bag; and removing the sealed bag from the vacuum chamber, wherein the pliable bag molds to a shape of the components. The vacuum may be maintained inside the sealed bag as desired, such as until the bonding agent has cured.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing wherein like reference numbers represent like parts of the invention.